Spark gaps are needed to produce high current pulses that are used, for example, for excitation of certain gas lasers (excimer lasers), to produce shock waves, for high speed machining of metal materials or for electromagnetic acceleration of missles and projectiles.
According to the state of the art, mostly three-electrode spark gaps are used as triggerable spark gaps where the third electrode is used for ignition at a precisely defined time (see R. Winkler, "High Speed Machining--Principles and Technological Use of Electrically Produced Shock Waves and Pulsed Magnetic Fields," VEB Verlag Technik Berlin, 1973, pages 52-76). In the buildup phase, spark gaps have an inductance on the order of about 30 nH/cm. This has a negative or limiting effect on the steepness of the current rise. Therefore, there have been attempts to simultaneously produce a number of parallel spark channels. For example, it is known in the state of the art that three-electrode spark gaps with several spark channels can be constructed (see N. Thomas Olson, J. Bandas, A. C. Kolb, J. Appl. Physics, 50 (1979), 7768, N. Seddon, P. H. Dickinson, Rev. Sc. Instr., 58 (1987), 804).
One disadvantage of such three-electrode spark gaps is that they are limited to a relatively narrow operating voltage range which must be slightly below the breakdown voltage and can be adjusted by varying the electrode spacing and/or the gas pressure.
This disadvantage is avoided with the two-electrode spark gaps known according to the state of the art whereby a high voltage pulse with steep flanks is applied to the electrodes for the purpose of ignition. With such two-electrode spark gaps the operating voltage range extends down to extremely low voltages. The high voltage pulse needed for ignition, however, necessitates introduction of a decoupling inductance into the supply line to the energy source and/or to the load but this has an interfering effect in generating high current pulses with steep flanks. In order to ameliorate the interfering influence of the decoupling inductance, there have been attempts to use a ferrite material that can be saturated for the decoupling inductance. Essentially only a single spark channel is produced between the electrode pair with this type of spark gap.
It is also known according to the state of the art that a two-electrode spark gap can be ignited by the action of ionizing radiation on the space between the electrodes. Suitable ionizing radiation here would be a radioactive corpuscular or electromagnetic radiation in the form of X-rays or laser beams (see R. Winkler, supra). In addition, according to this literature reference, ignition of a spark gap can also be accomplished by triggering photoelectrons or thermal electrons by applying a sufficiently strong UV pulse or laser pulse to the cathode so these photoelectrons or thermal electrons can then serve to ignite the spark gap. These processes are tedious and dangerous to use and they necessitate an extremely high structural expense so they have not been successful in practice. Furthermore, the operating voltage with this spark gap must be close to the breakdown voltage.
A triggerable spark gap has been proposed wherein the electrodes are mounted on opposite walls of a microwave waveguide to which a microwave generator (magnetron) is attached, generating high power microwave pulses. The voltage applied to the electrodes--as with most of the spark gaps discussed above--is slightly below the breakdown voltage. When the microwave pulse is coupled into the waveguide, the microwave field distorts the electric field between the electrodes in such a way that sparking between the electrodes occurs, but here again only one spark channel is usually formed. This spark gap has the disadvantage that it functions satisfactorily only in the immediate vicinity of the breakdown voltage. This breakdown voltage may change rapidly, however, e.g., due to burnup of the electrodes, due to different geometric relationships or due to the pressure of the gas between the electrodes. For further information regarding the structure and operation of such a triggerable spark gap, reference may be made to U.S. Pat. No. 4,477,746, the teachings of which are incorporated by reference herein. Because of the close proximity of the operating voltage to the breakdown voltage and the frequent positive or negative variations that occur in the breakdown voltage, there is the danger of outage and/or misfiring with these previously known spark gaps.